Communication devices such as User Equipment (UEs) are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two UEs, between a UE and a regular telephone and/or between a UE and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network. Communication devices may herein also be referred to as network devices. UEs may further be referred to as wireless terminals, mobile terminals and/or mobile stations, mobile telephones, cellular telephones, laptops, tablet computers or surf plates with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless terminal or a server.
In some embodiments herein, the non-limiting term network device is used and it may refer to any type of wireless device communicating with a radio network node in a cellular or mobile communication system, such as e.g. an User Equipment (UE). Examples of UEs are target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine (M2M) communication, PDA, iPAD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles etc.
The communications network covers a geographical area which is divided into cells, wherein each cell is being served by one or more transmission points. A cell is a geographical area where radio coverage is provided by a transmission point. One or more cells may also have an overlapping cell area.
A network node may control one or more Radio Access (RA) nodes comprising one or more transmission points, e.g. having Radio Units (RRUs). A RA node may thus control one or more transmission/reception points. A transmission point, also referred to as a transmission/reception point, is an entity that transmits and/or receives radio signals. The entity has a position in space, e.g. an antenna. A network node is an entity that controls one or more transmission points. The transmission point may e.g. be a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node, Base Transceiver Station (BTS), Radio Access (RA) node. The network node may e.g. also be a base station such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node, Base Transceiver Station (BTS), Radio Access (RA) node, depending on the technology and terminology used. The network node could however also be a distributed node comprised in a cloud and being configured to control the transmission point from a distance. In some embodiments herein, the non-limiting term radio network node or simply network node is used and it may refer to any type of network node serving a UE and/or connected to another network node or a network element or any radio node from where a UE receives signals. Examples of radio network nodes may e.g. be Node B, base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNode B, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS) etc.
The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
Further, each network node may support one or several communication technologies. The network nodes communicate over the air interface operating on radio frequencies with the UEs within range of the network node. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction, i.e. from the UE to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks. In LTE the cellular communication network is also referred to as Evolved Universal Terrestrial Radio Access Network (E-UTRAN).
Multiple Input Multiple Output (MIMO), is an advanced antenna technique to improve the spectral efficiency and thereby boosting the overall system capacity. The MIMO technique uses a commonly known notation (M×N) to represent MIMO configuration in terms of the number of transmit (M) and receive antennas (N). The common MIMO configurations used or currently standardized for various technologies are: (2×1), (1×2), (2×2), (4×2), (4×4), (8×2), (8×4) and (8×8). The configurations represented by (2×1) and (1×2) are special cases of MIMO and they correspond to transmit diversity and receiver diversity respectively. Current LTE and HSPA standards support the use of a 1-dimensional array of co- or cross-polarized antenna ports. Under development in 3GPP is a standard support for 2-dimensional antenna ports, where antenna ports are located in both vertical and horizontal dimensions. In future systems the support for antenna ports may be drastically increased.
Multiple antennas employed at the transmitter and receiver may significantly increase the system capacity. By transmitting independent symbol streams in the same frequency bandwidth, which may also be referred to as Spatial Multiplexing (SM), a linear increase in data rates with the increased number of antennas may be achieved. Further, by using space-time codes at the transmitter, reliability of the detected symbols may be improved by exploiting the so called transmit diversity. Both these schemes assume no channel knowledge at the transmitter, such as e.g. a network node.